1. Technical Field
The present invention relates generally to fabricating capacitive micromachined ultrasonic transducers (“CMUTs”), CMUT imaging arrays, and electrical interconnect structures for catheter based devices using CMUT imaging arrays.
2. Background of Related Art
CMUTs combine mechanical and electronic components in very small packages. The mechanical and electronic components operate together to transform mechanical energy into electrical energy and vice versa. Because CMUTs are typically very small and have both mechanical and electrical parts, they are commonly referred to as micro-electronic mechanical systems (“MEMS”) devices. CMUTs, due to their miniscule size, can be used in numerous applications in many different technical fields, including medical device technology.
One application for CMUTs within the medical device field includes soft tissue and vascular imaging. This type of imaging can be carried out using an array with CMUTs mounted, for example, on a flexible catheter. The quality of the image produced is somewhat dependent on the size of the array, the acoustic power radiated to the medium, and the control over certain components of the CMUTs (e.g., diaphragm position) during transmission and reception of ultrasonic energy. The size of vessels that can be imaged using this technology, on the other hand, is limited by the size of the CMUT array and, accordingly, the catheter size. A smaller CMUT array enables smaller vessels and surrounding tissues to be imaged, reduces the obstruction of blood flow and makes it easier to maneuver.
In intravascular ultrasound (IVUS) imaging, it is important to have a small diameter catheter to image small coronary arteries. As a result, regardless of what technology is used (e.g., PZT or CMUT based arrays), the electrical interconnect scheme between the ultrasound array and the processing electronics becomes important in implementation, particularly for forward looking IVUS imaging. Since the forward looking IVUS catheter diameter is preferably on the order of 1-2 mm, it is desirable to use as much of the frontal area of the catheter as possible for ultrasound generation and reception. The use of a larger array can increase power levels and also improve image resolution.
CMUTs 100 manufactured using complementary metal-oxide-semiconductor (CMOS) manufacturing techniques are suitable for imaging very small blood vessels such as capillaries in terms of size. However, as shown in FIG. 1, significant numbers of connections 105 are required between the CMUTs 110 and the front-end electronics 115 through external, flexible interconnects 105. In addition, because the electronics 115 are generally manufactured on a separate chip, large numbers of these external connections 105 are required to connect each of the CMUTs to, for example, a duplexer. This results in a package 100 with an undesirably small CMUT 110 array, to keep the package small enough to be useful, or an array that is larger than necessary due to the external connections 105. In addition, these arrays 100 can also require a cover, or other structure, to cover the external wiring to prevent snags and damage to the subject artery.
What is needed, therefore, is a method for connecting the various electronic components in a manner that maximizes the CMUT array, while minimizing array cross-section using an internal connection scheme.
Additionally, there is a need in the art for fabricating CMUTs and CMUT arrays utilizing existing and inexpensive CMOS silicon chip manufacturing methods.
Additionally, the CMUT and associated electronics can be fabricated on the same chip, or on adjacent silicon layers, to minimize the number of external interconnects required.
Additionally, the transmit and receive electronics may require different CMOS processes, such as high voltage and low voltage processes, thus a compact interconnect scheme between the CMUT, low voltage CMOS and high voltage CMOS chips is needed while minimizing the overall size of an IVUS catheter.
It is to the provision of such CMUT fabrication and CMUT imaging array fabrication that the embodiments of present invention are primarily directed.